where to get replacement pots?

[RoyC]

>Please remember that the 24 ohm

>shunt is dividing current with the L-pad. At 1 ohm series

>resistance, twice as much current is going through the 24 ohm

>shunt than through the L-Pad shunt.

That's a good point! Nice graph! Actually the meter shows it to be more like the pot than the graph does.

This arrangement appears useful to past 1/2 rotation, well outside our range of interest. The only significant anomaly is that max or full "increase" results in 0 ohms in series and 25 ohms across the drivers (as opposed to 15 to 16 ohms with an AR pot), which could actually provide a desirable "boost" for folks who prefer more output (especially from the tweeter).

There really does not seem to be much downside to this arrangement after all. A couple of good quality 10 to 15 watt 24 or 25 ohm resistors can be acquired for a few bucks, and the new l-pads will last as long as new rheostats...and as I mentioned above, l-pads are easy to obtain and are already protected from stuffing.

Those interested in trying this out should be aware that l-pad terminals are not wired the same as AR pots:

-Wire to the AR pot's #2 terminal connects to the l-pad's #1 terminal.

-Wire to the AR pot's "B" terminal connects to the L-pad's #2 terminal.

-Wire to the AR pot's #1 terminal connects to the L-pad's #3 terminal.

-The resistor is wired at any point up to the driver as a shunt between the l-pad's #1 and #2 terminal wires.

Thanks Jerry...

Roy

[dynaco_dan]

Hi again and open to all members;

Could you please tell me what would happen if this Tru-Ohm 15

ohm 25 watt w-w pot was inserted into, say, an AR-4X, just for

a simple speaker circuit example.

I know that the outer terminal to speaker common would not be

connected.

This would still leave an adjustable resistance to the

tweeter, 0 -15 ohms.

With only 2 terminals I assume the one side is on the coil and

wiper blade is the other.

On a regular pot there is a terminal on each end of the coil

and one for the wiper.

Usually one end contact to speaker common, center to tweeter

and the other end to capacitor output.

The AR-2 tweeter was wired using only the outer and center

terminal connections of a 10 ohm 4.5 watt Clarostat w-w pot.

I do not have an AR-2A crossover handy to see if they also are

using only the center and one end terminal, presumably yes, at

least with the Clarostat pots.

The AR-2AX later version of crossover that I have has the

Aetna-Pollock pots and uses all 3 contacts.

The rear open view of the MicroStatic Tweeter Array speaker

photo shows another pot for those tweeters using only the

center and one outer terminal, leaving the other outer

terminal un-used.

If these two examples, assuming they were instead 15 ohm pots,

were to have the empty un-used terminal connected to the

speaker common what would happen?

Likewise, if the common connection of the pot in the AR-4X was

disconnected, what might happen?

[onplane]

>

>That's a good point! Nice graph! Actually the meter shows it

>to be more like the pot than the graph does.

>

>Thanks Jerry...

>

>Roy

>

Please remember, Roy, my plot was a theoretical plot based upon an ideal L-Pad. As John pointed out in another thread, L-Pads are very real devices and vary significantly from the ideal.

I don't doubt for a minute that actual measurements track closer to pots. From my perspective it makes little difference, because in the range of interest they track close enough even assuming an ideal device.

Roy, just two comments:

1. I think this L-Pad will be the ideal solution for the new tweeter as we'll really need a method to "pad"

2. You never mentioned the wattage of the 24 ohm shunt resistor. I'm thinking in the range of 10 watts as there is a measure of power dissipation sharing between the 24 ohm and the L-pad.

Regards,

Jerry

[RoyC]

>Please remember, Roy, my plot was a theoretical plot

>based upon an ideal L-Pad. As John pointed out in another

>thread, L-Pads are very real devices and vary significantly

>from the ideal.

It seems so...I just measured it again with a 25 ohm shunt. At 5 ohms series (past 1/2 l-pad rotation) I was still getting a "pot-like result"..with 11.5 ohms in parallel with the driver, and an overall (between #1 and #3) reading of 15.5 ohms.

>1. I think this L-Pad will be the ideal solution for the new

>tweeter as we'll really need a method to "pad"

Ken K. has the tweeters, so we will be getting some direction soon.

>2. You never mentioned the wattage of the 24 ohm shunt

>resistor. I'm thinking in the range of 10 watts as there is a

>measure of power dissipation sharing between the 24 ohm and

>the L-pad.

I'm currently using 15 watt 8 ohm l-pads, and 10 watt 25 ohm Dayton resistors purchased from Parts Express.

Roy

[onplane]

>Hi again and open to all members;

>

>Could you please tell me what would happen if this Tru-Ohm 15

>ohm 25 watt w-w pot was inserted into, say, an AR-4X, just

>for a simple speaker circuit example.

>

>This would still leave an adjustable resistance to the

>tweeter, 0 -15 ohms.

>

Hi, Vern!

I don't think your suggestion would be a total disaster. There WILL be a slight alteration in the frequency response of the tweeter, but whether you could hear or not ... well, that's another matter.

With the w-w pot set at zero, this would be identical to totally by-passing the pot.

My guess, however, is the vast majority of folks would set that pot at something in the range of 1 to 3 ohms and the difference between that and a pot set at 1 to 3 ohms would be fairly minor.

Regards,

Jerry

PS: My philosophy is kind of like Carl's. That is, try it!! Then compare to a speaker with a pot and see if you can hear any difference.

[Guest Ozmoid]

>With the w-w pot set at zero, this would be identical to

>totally by-passing the pot.

After playing with the PE L-pads for a while, I can say that's not what they do - there is no "0" setting at all that would match a straight wire. In the PE L-pad mentioned above, there is an 8ohm coil and a 40ohm coil, set opposite each other 8->0, 0->40. The MIN setting on the L-pad is 40ohms, the MAX setting on the L-pad is 8ohms.

Under the speaker load, all the readings change as well - I would certainly put the L-pad under the actual load it will see to get any readings. I learned the hard way that the speaker load will change what the L-pad "presents" to the rest of the crossover.

You can solder a small wire to the 8ohm end of the outer coil, and then use your DVM to determine where on the 40ohm coil the L-pad reads 16 ohms across terminals 1 and 3, and solder the other end there. Now clip the center wiper out of the control, and you have an 8ohm "pot" adjustable from 8 to 16 ohms.

Not the most elegant solution, but it works.

[onplane]

>

>

>>With the w-w pot set at zero, this would be identical to

>>totally by-passing the pot.

>

>After playing with the PE L-pads for a while, I can say that's

>not what they do - there is no "0" setting at all

>that would match a straight wire. In the PE L-pad mentioned

>above, there is an 8ohm coil and a 40ohm coil, set opposite

>each other 8->0, 0->40. The MIN setting on the L-pad is

>40ohms, the MAX setting on the L-pad is 8ohms.

>

>Under the speaker load, all the readings change as well - I

>would certainly put the L-pad under the actual load it will

>see to get any readings. I learned the hard way that the

>speaker load will change what the L-pad "presents"

>to the rest of the crossover.

>

Hi, ozmoid!

I think there is a little confusion here as I don't believe the w-w pot is an L-Pad nor is it a potentiometer. I think it's just a variable resistor. To the tweeter it will appear as a SERIES resistor that varies from zero to 16 ohms.

As for your L-pad in the wide open position, it's sort of in between a wide open pot and a totally by-passed tweeter pot.

Wide open pot net resistance: 2.16 ohms

Wide open L-pad net resistance: 2.35 ohms

Totally by-passed pot net resistance: 2.50 ohms

Roy's solution with the 25 ohm shunt:

Wide open L-pad w/shunt net resistance: 2.15 ohms

Ozmoid, would you please share with us your experience with speaker loads and L-Pads, as I'd like to learn how these are related and what can go wrong.

Regards,

Jerry

PS: Your wide open L-pad will yield slightly more sound output from the tweeter than a wide open pot. I haven't done the math, but I'd guess in the range of 0.5db. That 40 ohms just dissipates LESS energy than the 16 ohm pot.

[johnieo]

>The AR-2 tweeter was wired using only the outer and center

>terminal connections of a 10 ohm 4.5 watt Clarostat w-w pot.

>

>The AR-2AX later version of crossover that I have has the

>Aetna-Pollock pots and uses all 3 contacts.

>If these two examples, assuming they were instead 15 ohm

>pots,

>were to have the empty un-used terminal connected to the

>speaker common what would happen?

>

>Likewise, if the common connection of the pot in the AR-4X

>was disconnected, what might happen?

Vern:

Attached is a sketch of three X-O arrangements, one is the standard Pollak 3-terminal pot, the second is how a two-terminal rheostat would be wired.

**No, you would not want to connect the third terminal of the pot in a crossover such as shown in the right-hand sketch to anything except the wiper. Just leave it floating it does nothing. You could add a jumper as shown in dotted-red. To connect it to the tweet common would change the factory crossover.

**No, you would not want to disconnect the common pot connection in the AR-4x tweeter X-O either. To do so would really alter the phase/amplitude at crossover.

Jerry:

Your description of an L-pad is incorrect. When it is turned to its max clockwise position, the series resistance is zero and the parallel resistance is infinite. See first attached jpg. This is just ONE reason why L-pads do not perform the same as a potentiomenter. The 40-Ohm parallel resistor does not extend through the 300-degree rotation, but rather it ends at about ten degree before max CW rotation and is out of the circuit after that point.

Secondly your calculations and desctiptions to Roy and Shacky are not correct; see second attached jpg figure. You cannot simply add the parallel resistance value to the dc resistance of the voice coil and calculate db loss or gain; Rvc it is just part of the tweeter, you must also consider Lvc. It is more complex than you describe--the equivalent R', L' of Rp||(Rvc+Lvc) are shown; each equivalent value is a function of three variables. Note also that removing the Rp changes the phase angle at crossover and thus changes the way the mid and tweet signals add at crossover; that's another reason why the sound is different than a potentiometer.

IMO this discussion has gone the same way as your previous biamp crusade. People have either removed the pot, or will never do so. New pots are available--yes they cost 20$, but they are available. Alternatively, if one does not want to spring for a new pot, one can install an L-pad with a fixed resistor across terminals 1-2 as suggested by Roy C., and have an attenuator that reasonably mimics a pot in the range of normal use.

I also note you have had this same conversation on Audiokarma with the same irreconcilable differences of opinion. Based on off-CSP e-mail, you might well consider ending this discussion and moving on.

[onplane]

>

>Jerry:

>

>Your description of an L-pad is incorrect. When it is turned

>to its max clockwise position, the series resistance is zero

>and the parallel resistance is infinite. See first attached

>jpg. This is just ONE reason why L-pads do not perform the

>same as a potentiomenter. The 40-Ohm parallel resistor does

>not extend through the 300-degree rotation, but rather it ends

>at about ten degree before max CW rotation and is out of the

>circuit after that point.

John, when I ran the plot for Roy (back in message #24) I assumed that the L-Pad was open when series resistance = 0.

Ozmoid in post #30 said that at the minimum psetting (series resistance =0) he got on his PE L-Pad for the parallel coil was 40 ohms, so that's what I used.

John, if this is NOT correct, I would say that an L-Pad in the max position (when series resistance = 0) is then identical to completely by-passing the pot. I really don't know what's going on with ozmoid's L-Pads and assumed he knew what he was doing when he measured.

>

>Secondly your calculations and desctiptions to Roy and Shacky

>are not correct; see second attached jpg figure. You cannot

>simply add the parallel resistance value to the dc resistance

>of the voice coil and calculate db loss or gain; Rvc it is

>just part of the tweeter, you must also consider Lvc. It is

>more complex than you describe--the equivalent R', L' of

>Rp||(Rvc+Lvc) are shown; each equivalent value is a function

>of three variables. Note also that removing the Rp changes the

>phase angle at crossover and thus changes the way the mid and

>tweet signals add at crossover; that's another reason why the

>sound is different than a potentiometer.

John I don't agree with your model because it assumes that Ls and Rs are constants, which they are NOT. The problem becomes considerably more complex when dealing in the real world with real devices.

Your equivalent model for a speaker is woefully inadquate. As frequency rises so does the Rs, but at the same time Ls decreases. This means the phase angle is also NOT a constant. John, here is an article describing a more complete speaker model:

http://www.epanorama.net/documents/audio/s..._impedance.html

John I looked for the series resonant induced spike you predicted and could find NOTHING! Not even a blip. My belief is once again the model fails to take into account the real dynamics of a speaker.

In any event, Ken is measuring some tweeters and shortly we'll all know what's really going on. Hopefully, then we'll all be able to build better models that will allow us to predict more accurately the real world.

>IMO this discussion has gone the same way as your previous

>biamp crusade. People have either removed the pot, or will

>never do so. New pots are available--yes they cost 20$, but

>they are available. Alternatively, if one does not want to

>spring for a new pot, one can install an L-pad with a fixed

>resistor across terminals 1-2 as suggested by Roy C., and have

>an attenuator that reasonably mimics a pot in the range of

>normal use.

Well, John, you negelected the 3rd option of simply by-passing the pot wipers. Clearly a viable option and one I recommend.

Next, IF folks choose the removal route for one of the pots, I recommend that they choose the better of the two (from a condition standpoint) for the pot that remains. Clearly an economical option.

Naturally, John, I am NOT a big fan of speaker controls when one can move the controls back to the amps, but I no longer recommend bi-amping to new owners of AR's or people unfamiliar with electronics.

One final thought, if one really is in "love" with the notion of speaker controls, I would recommend the external solution that one creative individual recently described in a post here. I seriously doubt that you can prevent corrosion when you have heat, current and dissimilar metals. Corrosion will change the voicing of our AR's as it adds resistance where none was intended.

So why not mount the controls in a location that allows for easy maintenance?

Regards,

Jerry

[dynaco_dan]

Hi John;

Thank you very much for responding to my questions.

The AR-2 tweeter was wired using only the outer and center (wiper) terminal connections of a 10 ohm 4.5 watt Clarostat w-w pot.

The coil end terminal on the Clarostat pot was not connected (floating).

In Carl's case, can he use his four, Tru-Ohm 2 terminal 15 ohm w-w pots in the AR-2, in this example, disregarding the 10 ohm and 15 ohm differential?

I will assume so with slight resistance difference only.

This question is also being asked for anyone with the same or similar pots on hand.

The AR-2AX later version of crossover that I have has the

Aetna-Pollock pots and uses all 3 contacts.

If these two examples, assuming they were instead 15 ohm pots,

were to have the empty un-used terminal connected to the speaker common what would happen?

Likewise, if the common connection of the pot in the AR-4X was disconnected, what might happen?

>Vern:

Attached is a sketch of three X-O arrangements, one is the

standard Pollak 3-terminal pot, the second is how a

two-terminal rheostat would be wired.

John what program did you use for your drawings, please?

**No, you would not want to connect the third terminal of the

pot in a crossover such as shown in the right-hand sketch to

anything except the wiper. Just leave it floating it does

nothing.

You could add a jumper as shown in dotted-red.

We'll disregard the dashed red jumper.

To connect it to the tweeter common would change the factory

crossover.

Can you state what changes there may be, please, John?

**No, you would not want to disconnect the common pot

connection in the AR-4x tweeter X-O either. To do so would

really alter the phase/amplitude at crossover.

Could you more clearly re-state the previous comment, John.

Thank you for coming forward, John.